Electronic stability control systems are available for use on commercial vehicles such as truck/tractor trailers and buses. These stability systems monitor the dynamic operation of the vehicle and intervene when needed to provide rollover stability or yaw stability.
Rollover stability counteracts the tendency of a vehicle, or vehicle combination, to tip over while turning. The lateral (side) acceleration during turning creates a force at the center of gravity (CG) of the vehicle, “pushing” the vehicle horizontally. The friction between the tires and the road opposes that force. If the lateral force is high enough, and the tire cornering forces has not yet saturated, the centrifugal force on the CG can create rotational moment at the outer wheels. As a result, one side of the vehicle may begin to lift off the ground potentially causing the vehicle to roll over.
Yaw stability counteracts the tendency of a vehicle to spin about its vertical axis. During operation, if the friction between the road surface and the vehicle's tires is not sufficient to oppose lateral forces, one or more of the tires can slide, causing the vehicle to spin.
Electronic stability systems typically utilize an electronic control unit (ECU) that includes system control logic and receives operational information, such as wheel speed, lateral acceleration, yaw rate, and steering angle sensors, from various sensors. The information from these sensors allows the control unit to identify when a stability risk occurs. A single control tuning, which is customized for a particular vehicle family or platform, is typically uploaded to the system ECU at the vehicle manufacturer. For this particular vehicle platform, the single customized control tuning defines which combinations of sensor readings (i.e. intervention thresholds) will result in the ECU taking corrective action due to a calculated stability risk. If the thresholds are exceeded, the system intervenes to assist the driver in maintaining stability.
In addition, some stability system logic may be somewhat adaptive. For example, the system may receive operational information on the vehicle load, such as whether the vehicle is hauling an empty trailer or is hauling a loaded trailer. The adaptive aspect of the system may modify the intervention thresholds for a loaded trailer such that the thresholds may be different than the intervention thresholds for an unloaded trailer. Since the system for a particular vehicle platform has a single customized tuning, however, if the operating conditions are the same, the vehicle intervention thresholds will happen in the same manner (i.e. with the same sensitivity).
In the case of a potential roll event, the system may intervene by overriding the throttle and quickly applying brake pressure at selected wheels to slow the vehicle before the lateral acceleration reaches a critical level. In the case of vehicle slide, the system may reduce the throttle and then brake one or more of the “four corners” of the vehicle (in addition to potentially applying the trailer brakes), thus applying a counter-force to better align the vehicle with an appropriate path of travel.
Some commercial vehicles, however, may be used in a variety of vehicle configurations or conditions, which may result in different vehicle dynamics. For example, a tractor may need to haul a single trailer for one job and haul a double or triple trailer combination for another job. A tractor hauling a double or triple trailer combination may have more tendency to rollover or slide than a tractor with a single trailer under the same dynamic conditions. Since the single tuning of the system is optimized for one vehicle configuration or condition, the stability system may not intervene optimally when the vehicle's configuration or condition is changed. Thus, the safety and drivability of the vehicle may be suboptimal when the vehicle configuration/condition is different.